Rotor / Rotor Aerodynamic Interactions – a GARTEUR Action Group

The paper presents the objectives, the activities and the results obtained in a self-funded research project carried out by the AG-25 “Rotor-rotor wakes Interactions” consortium of the Rotorcraft Group of Responsables in the GARTEUR framework. The formation of this Action Group was motivated by the observation that new high-speed compound and multi-rotor rotorcraft concepts are spreading out and aerodynamic interactions between rotating parts is important for vehicle performance and stability, especially at low speed. However, there are very few experiments available to improve the understanding and consequences of such interactions and to validate and improve numerical methods. Three research centers: ONERA (France), CIRA (Italy), DLR (Germany), and four universities: Politecnico di Miliano (PoliMi) (Italy), University of Glasgow (UoG) (United Kingdom), National Technical University of Athens (NTUA) (Greece) and University of Stuttgart (IAG) (Germany), joined their efforts to fill this gap through common research activities. In particular, three experimental investigations were conducted to study different kinds of rotor / rotor interactions. Two are representative of a fast rotorcraft similar to the Airbus Helicopter RACER, and one of a multicopter vehicle. The measurements include loads on the rotating parts, PIV in the flowfield, as well as noise radiation. The numerical activities aimed at reproducing most of the experimental matrices and comparing different levels of fidelity (ranging from BEM tools up to unsteady RANS CFD). The outcomes of this study are the acquisition of experimental databases and a better understanding of the physics of rotor / rotor interactional aerodynamics. Furthermore, there is a significant validation and improvement of the current numerical tools, and extraction of best practices for the prediction of future high speed and multicopter rotorcraft performance, noise and stability.